Method and apparatus for measuring and controlling the thickness of a filament or the like

ABSTRACT

A light beam, such as that obtained from a laser, is irradiated onto a fine filament of wire, yarn or the like to produce a diffraction pattern. The spacing between the light and dark portions of the diffraction pattern is measured to provide an indication of the diameter of the filament. Several means for measuring the diffraction pattern spacing are disclosed. Also disclosed is a method of utilizing an interference pattern produced by irradiating a sharp edge with a light beam, thereby to evaluate the edge sharpness.

United States Patent 91 Kruegle 1 Jan. 9, 1973 [54] METHOD AND APPARATUSFOR MEASURING AND CONTROLLING THE THICKNESS OF A FILAMENT OR THE LIKE[75] inventor: Herman A. Kruegle, River Vale,

[73] Assignee: Holoheam, Inc., Paramus, NJ.

[22] Filed: May 20, 1970 [21] Appl. No.: 38,968

[52] US. Cl. ..356/l60, 356/111, 356/69 [51] Int. Cl ..G0lb 11/04, GOlb9/02, GOlb 11/24 [58] Field of Search ..356/69,159,106, 71,160

[56] References Cited UNITED STATES PATENTS 3,518,007 6/1970 [to..356/l62 Averaging 3,503,687 3/1970 Venema ..356/l06 PrimaryExaminer-Ronald L. Wibert Assistant Examiner-Conrad ClarkAttorney-Sandoe, Hopgood and Calimafde [57] ABSTRACT A light beam, suchas that obtained from a laser, is irradiated onto a fine filament ofwire, yarn or the like to produce a diffraction pattern. The spacingbetween the light and dark portions of the diffraction pattern ismeasured to provide an indication of the diameter of the filament.Several means for measuring the diffraction pattern spacing aredisclosed. Also disclosed is a method of utilizing an interferencepattern produced by irradiating a sharp edge with a light beam, therebyto evaluate the edge sharpness.

2 Claims, 17 Drawing Figures Detector Signal Computer PATENTED JAN 9I973 SHEET 1 0F 4 LASER EAM LASER BEAM d FIG.2

D EET R Molten Material user Defec'ror Array II m 0 e u D LE. e I I I:ml "w a I INVENTOR. H6. 4 Hermon A.Krue'gle TTORNEYS PATENTEDJAH 9 I975SHEET 2 BF 4 suzcrnomcs LASER BEAM2 F l G. 5 i

LASER Yarn Electronics LASER BEAM 66 Detector Yarn Feedback Signal I 72Readout Kw N. me u u R N 0 EK T T n O m a a H 1 I e m e 6 w 6 D m b w MG w/ F o 2 6 E RO l e LB M Y PAIENTEUJAH' 9 I975 SHEET 3 on;

2 76 )8?" Laser m l 3 86 78 2 74 Raw 3 g f Coahng Machine V O b T 88 198 92 [Eerecfor comparaf k Detector 4 /90 f 94 lElecfronu ghicknessgectmmcs Jo Wire Forming ompute' \96- Apparatus Screen I00 20 Laser Yarn24 Diffraction FIG u Laser Motor I Detectar Signal -Averaging ComputerINVENTOR. FIG '2 Herman A.Kruegle ATTORNEYS METHOD AND APPARATUS FORMEASURING AND CONTROLLING THE THICKNESS OF A FILAMENT OR THE LIKE Thepresent invention relates to a method and apparatus for measuring thediameter of a yarn or wire filament, or the like.

It is often necessary to be able to measure the diameter of a fine wire,yarn, filament or the like, particularly during the manufacturingprocess of such articles. For example, in the process of forming fineyarn having a predetermined denier or diameter, the yarn is extrudedfrom a molten supply of thermo-plastic material such as by a spinerette,from which the material is then removed at a specified rate andcollected at a suitable take-up roll. Thus, measurement of the yarnthickness usually must be made while the yarn is moving between itsinitial forming station and its eventual collection station. Similarly,in the fabrication of fine wire, it is usually necessary to maintain thediameter of the wire to within close tolerances. The wire fabricatingprocess is often complicated by a requirement that the wire be coatedwith a suitable insulating material wherein it is necessary to maintainthe overall diameter of the raw wire and its coating to within aprecisely specified measurement. As in the case of yarn, measurement ofthe wire diameter usually must be made while the wire is in motionbetween its various stages of formation and collection.

Several approaches have generally been taken in the measurement of thediameter of fine diameter filaments. The first of these is essentiallymechanical in nature and generally includes the use of a feeler devicewhich contacts the moving filament to provide the diameter measurement.The deficiencies of measurement devices of the feeler type primarilyresult from the difficulty in providing sufficiently fine feeler devicesfor use with correspondingly fine or narrow filaments, and because thecontact of the feeler and the filament may cause a distortion in theshape and dimension of the filament. Another approach used in thetextile industry is to measure the weight of a known length of yarnhaving a known specific gravity. The result is expressed in deniers. Thedifficulty with this method is that it is time consuming and not realtime. Another method is by use of a capacitometer in which the sensorresponds to the volume of dielectric material (yarn) between twocapacitor plates. This method is inaccurate since the measurementobtained is a function of water vapor content. Another method is tomeasure the attenuation of beta rays caused when the yarn is put betweenthe source of beta rays, and the beta ray sensor. This method too is notsufficiently accurate. Another basic approach to the measurement offilament involves the use of a light beam in combination with an opticalmeasuring system which may be characterized as non-contacting in nature,that is, no mechanical device is used to contact the filament. Whilethis approach avoids some of the problems resulting from the mechanicalsystems, the optical systems are usually highly complex in nature, anddo not readily lend themselves to the measurement of extremely finediameter filaments as a result of errors in troduced in the measurement,as a result of noise signals, and the like. Errors in measurement mayalso be introduced in both the contacting and non-contacting systems asa result of relatively minor lateral movement of the filament as itpasses through the measurement system.

It is an object of the present invention to provide an improvedapparatus and method for measuring the diameter of a filament.

It is another object of the present invention to provide an apparatusand method for measuring filament diameter with great accuracy.

It is a further object of the present invention to provide a method andapparatus for measuring the diameter of a moving filament in which thefilament is not contacted during the measurement operation, and in whichthe diameter is extremely accurate even for relatively fineor smalldiameter filaments.

It is another object of the present invention to provide an apparatusand a method for measuring the diameter of a filament of the typedescribed in which the result of the measurement can be readily providedand which can be used to control the filament forming operation ifdesired.

It is a general object of the invention to provide an apparatus and amethod for measuring the diameter of a small diameter moving filament byuse of a relatively uncomplicated and reliable system which providesmeasurements of high accuracy and repeatability.

Broadly considered, the present invention provides a method andapparatus for measuring the diameter of a filament in which a light beamis caused to be incident of the filament, to thereby provide adiffraction pattern comprising alternating dark and light areas. Bymeasuring the spacing between corresponding ones of these dark or lightareas, an accurate determination of the diameter of the filament can bemade by solving an equation in which the only unknown is the filamentthickness. The other factors in that equation which are known includethe bandwidth of the incident light beam, and the distance of thefilament from the plane on which the diffraction pattern is formed.

Disclosed herein are several examples of means for accurately detectingor sensing the spacing between the diffraction pattern areas. Alsodisclosed is a system for measuring the thickness of an insulatingcoating formed on a wire, and for controlling the coating process inresponse to the measurement of the combined diameter of the wire and thecoating.

The present invention further discloses the use of a laser light beam inthe testing of the sharpness of an edge such as on a blade or a needle,by irradiating the sharpened edge with a laser beam and detecting theinterference pattern produced as a result of that radiation. For arelatively sharp edge, the interference pattern produced is uniform innature and has clearly defined dark and light patterns, while for arelatively dull edge, the diffraction or interference pattern isirregular and spread out in a non-uniform manner. The interferencepattern may be used either to monitor the edge sharpening operation or,if desired, to control the sharpening operation upon the sensing of aninterference pattern indicative of an insufficiently sharpened edge.

To the accomplishment of the above and to such other object as mayhereinafter appear, the present invention relates to a method andapparatus for measuring the diameter of a filament or the like,substantially as defined in the appended claims, and as described in thefollowing specification taken together with the accompanying drawings inwhich:

FIG. 1 is a schematic diagram illustrating a. diffraction patternobtained by passing a light beam through a narrow slit for the purposeof explaining the principles of the invention;

FIG. 2 is a schematic diagram similar to FIG. 1, illustrating theformation of a diffraction pattern by the irradiation of a filament witha laser beam to further illustrate the basic principle of the presentinvention;

FIG. 3 is a schematic representation of a filament forming operation inwhich the diameter of the filament is measured in accord with thepresent invention;

FIG. 4 is a detailed schematic diagram of the method and apparatusillustrated in FIG. 3 showing one embodiment of a diffraction patternsensing device that can be used with the apparatus of FIG. 3;

FIG. 5 is a schematic diagram illustrating a second detector for use insensing the diffraction pattern in accord with the practice of thepresent invention;

FIG. 6 illustrates schematically yet another embodiment of a diffractionpattern sensing device for use in the practice of the present invention;

FIG. 7 is a view similar to FIGS. 4 6 illustrating yet another possibledevice for sensing the diffraction pattern obtained in the practice ofthe invention;

FIGS. 80 and 8b are, respectively, a side elevation and a plan view ofyet another diffraction pattern sensing device for use in the practiceof the invention;

FIG. 9 graphically illustrates a typical signal derived from thediffraction pattern sensing device of FIG. 8;

FIG. 10 is a schematic diagram of an apparatus for measuring thediameter of a coated wire in which the principles of the presentinvention are employed;

FIG. 11 illustrates schematically a further embodiment of the presentinvention in which the diffraction pattern is obtained by the reflectionof a beam from the filament;

FIG. 12 illustrates in schematic form a system for measuring thediameter of a filament using the basic principles of the embodiment ofFIG. 11;

FIG. 13 illustrates schematically a further embodiment of the presentinvention;

FIG' 14 illustrates schematically the practice of the present inventionin testing the sharpness of an edge;

FIG. 15 illustrates the diffraction pattern obtained from the apparatusof FIG. 14 for an edge having a high degree of sharpness; and

FIG. 16 is a corresponding diffraction pattern obtained from theapparatus of FIG. 14 in which the edge being tested is relatively dull.

The method and apparatus of the invention make use of the diffractionpattern produced when a light beam is incident on a filament such as ayarn or wire, to provide a measurement of the diameter of the filament.By measuring the spacing between the dark and light areas of thatdiffraction pattern the diameter of the filament may be obtained bysolving an equation in which the filament diameter is only unknown. Thisequation may be derived by an examination of the diffractionpatternproduced by the system schematically illustrated in FIG. 1.

As illustrated in FIG. 1, a beam of light having a known wavelength A isincident upon a plane 10 in which two slots S1 and S2 vertically spacedby a distance d are formed. An image plane 12 is located at a distance Dfrom plane 10 and as is known, a diffraction pattern, including aplurality of alternating bright regions 14 and dark regions 15, isproduced on image plane 12 as a result of the passing of the light beamthrough those spaced slots. The distance between the adjacent brightregions 14 (and the dark regions 15) formed on image plane 12 isdesignated A y.

From Braggs law of diffraction it is known that dsina m A (l) where m0,1, 2,... the multiple values of m representing the multiple spacedbright regions produced in the diffraction pattern, and a is the angleshown in FIG. 1 between the direction of the light beam and thediffraction pattern region. From an analysis of the geometry of FIG. 1,assuming that A y is substantially smaller than D, and tan a isapproximately equal to sin a, we obtain A y Dsin a (2).

Substituting for sin a in equation (2), we then obtain )t=dAy/mDord=kmDlAy (3).

Thus, as indicated in equation (3), the distance of d between the slotsS1 and S2 in plane 10 can be determined from a knowledge of Ay, thespacing between corresponding regions of the diffraction pattern, sincethe other variables in equation (3), that is It, m and D are known.

The principles of the present invention as illustrated in FIG. 2 arebased primarily on the above described phenomena in which the verticallyspaced slots in plane 10 are replaced by the diameter of a filament,yarn or wire 16, on which a light beam having a wavelength A is incidentto produce the diffraction pattern on screen 17 much in the manner as inFIG. 1. It is recognized that the diffraction phenomenon is morecomplicated than described above in the case of the yarn. This is sobecause the yarn is transparent and hence produces diffraction patternscaused by light that has (I) diffracted around the yarn filament (2)internally reflected through the yarn, and (3) reflected light from thesurface of the yarn. The system of FIG. 2 thus represents in its mostbasic form, the use of a diffraction pattern to obtain the measurementsof the diameter of filament 16 in accord with the present invention inwhich the yarn diameter is given by the expression in equation (3). Itis noted that to solve equation (3) a knowledge of the wavelength A ofthe incident light beam is required to calculate the diameter of thefilament. For this purpose it is preferable that the light beam used toform the diffraction pattern be monochromatic in nature and have areadily determinable wavelength, so that the light beam isadvantageously obtained from a laser (not shown in FIG. 2), whichproduces an intense monochromatic beam of light as a known wavelength.

FIG. 3 illustrates the practice of the present invention in themeasurement of the diameter or thickness of a quantity of yarn as it isbeing produced. As is conventional, a quantity of molten thermoplasticmaterial is processed in a spinerette 18 to produce a fine yarn 20 whichis then passed between a pair of rollers 22, thereby to remove the yarnfrom spinerette 18 in a conventional manner. A laser 24 is positionedalong the path of movement of yarn 20 and produces a light beam 26 whichis incident upon yarn 20 in a direction perpendicular to its movement.Light beam 26 is interrupted by yarn 20, thereby to produce adiffraction pattern which is sensed at a detector 28 in which the spacing between the dark and bright regions of that diffraction pattern aremeasured. That spacing information is subsequently used to automaticallycompute the diameter of yarn in accord with equation (3).

FIGS. 4 8 illustrate various types of detectors which can be employed inthe practice of the present invention to measure the spacing between thebright and dark areas on the diffraction pattern. That information canthen be converted into signals for use in computing the yarn diameteraccording to equation (3) by appropriate electronic computing circuitryof the type well known in the art and which is thus not more completelydescribed in this application.

For example, the detector 28a shown in FIG. 4 comprises an array ofspaced, light-sensitive detectors 30 arranged along the plane of thediffraction pattern formed when laser beam 26 is incident upon yarn 20.The location of the bright and dark regions of that diffraction patterndetermines which of detectors 30 are energized, or which part of alinear detector, which may be used instead of the array of individuallight detectors 30, is irradiated by the diffraction pattern brightregions. That information can be converted into signals representativeof the distance between these bright regions, which signals in turn areapplied and processed in an electronic computing system generallydesignated 32 to provide the computed indication of the diameter of yarn20 as desired. Computing system 32 may be modified along known lines toproduce an output signal representative of the yarn diameter which couldbe ap plied to a process control system (not shown in FIG. 3) to controlthe yarn fabrication operation, thereby to maintain the yarn diameter atsubstantially its desired value.

In the embodiment of the invention shown in FIG. 5, the detector 28b isin the form of a scanning detector 34 which is caused to rotate past theplane of the diffraction pattern at a rate w. Since the angular velocityof detector 34 is known, the spacing Ay between the bright regions 14 onthe diffraction pattern corresponds to the time interval between thedetection of the adjacent bright regions. That time interval can beconverted, by any suitable means known in the art, into a signalproportional to A y, that signal in turn then being processed incomputing system 32 as indicated above, to compute the thickness of theyarn.

The system illustrated in FIG. 6 is useful for obtaining measurement ofthe diameters of a plurality of yarns 20 by the use of a single beamderived from laser 24. That beam is incident upon a rotating mirror 35connected to a shaft 36, which in turn is caused to rotate by a motor38. The rotating mirror 35 causes the laser beam to be scanned in acircular plane perpendicular to the longitudinal axes of the yarns, thuscausing the diffraction patterns to be produced across a plurality ofdetectors positioned behind their respective yarns 20. Detectors 40sense the spacing between the bright regions of the diffraction patternsformed by the incidence of the rotating laser beam on their respectiveyarns, to produce in a manner similar to that described above, suitablesignals for computing the respective yarn diameters.

In the embodiment of FIG. 7, the diffraction pattern spacing detector isin the form of a rotating drum 42 having a series of spaced, taperedopenings 44-48 formed about its outer periphery. A fixed linear detector50 is positioned in the interior of drum 42 in alignment with thediffraction pattern formed by the interference of the laser beam '26 byyarn 20. The vertical dimensions of the tapered openings varysubstantially linearly along their extent so that as drum 42 rotatespast the diffraction pattern, a continuously varying vertical opening isprovided immediately behind the diffraction pattern.

Linear detector 50 receives images through these openings and has itsupper and lower ends respectively connected to terminals 52 and 54across which a voltage E is developed. That voltage is proportional tothe light incident upon detector 50, and as drum 42 rotates, voltage Ewill vary and be at a maximum when the instantaneous spacing between thebright regions 14 of the diffraction pattern equals or matches thevertical spacing between tapered openings 44-48 on drum 42. The sensingof a maximum voltage E thus corresponds to a unique rotational positionof drum 42 and one value of vertical spacing between the taperedopenings. That value in turn represents the spacing between the brightregions of the diffraction pattern which information may be utilized andcomputed as described above to obtain a precise measurement of the yarndiameter.

FIGS. 8a and 8b are respectively elevation and plan views of a systemfor detecting the spacing between the bright spots on the diffractionpattern in which the detector is in the form of a rotating cylinder 56which is caused to rotate at an angular velocity w by a motor 58. Aplurality of spaced axial, narrow slits 60 are formed in the wall ofcylinder 56. The diffraction pattern produced by the interference of theyarn on the incident laser beam is caused to be incident on a mirror 62to produce an image of the diffraction pattern on the interior surfaceof cylinder 56. A lens 64 is positioned external to cylinder 56intermediate rotating slots 60 and a detector 66, the output of which isconnected to a computing system 68. Detector 66 senses, in a mannerdescribed below, the spacing between the bright regions on the reflecteddiffraction pattern and applies that information to computer system 68for calculating with great accuracy the diameter of yarn 20 as indicatedabove. The output of computing system 68 may be applied to a visualread-out 70 which may be advantageously a photo-tube, digital display orthe like, to provide a readily comprehended indication of the yarndiameter.

A signal proportional to the yarn diameter may also, as shown in FIG.8a, be applied to the control portion of a feedback control network 72where it is compared to a reference signal to produce an error orcontrol signal. The latter signal is then processed in a known manner tovary the yarn processing operation, to thereby maintain the yarndiameter substantially at its desired value.

In the operation of the system of FIG. 8, as cylinder 56 rotates, andslit 60a moves from position a to position b (FIG. 8a), the outputvoltage of detector 66 will be a function of the image intensity of thediffraction pattern as illustrated by the waveforms shown in FIG. 9 inwhich the three peaks 74, 76 and 78 respectively correspond to the imagepositions 1, 2 and 3 shown in FIG. 8a. That waveform can be analyzed incomputer system 68 along with the known value of w, the angular velocityof drum 62, to provide the desired diffraction pattern spacinginformation required to obtain the measurement of the yarn diameter.

The measurement system illustrated schematically in FIG. permits themeasuring and controlling of the thickness of a coating placed on a wireor a thread such as when a conductive, metallic wire 80 is coated withan insulating layer. The measuring system comprises a pair of lasers 82and 84. The former is positioned along the path of movement of wire 80prior to the coating operation, and the latter is positioned along thepath of movement of the wire after the insulating coating has beenplaced thereon as the raw wire passed through a wire coating apparatus86.

The beam from laser 82 incident on the smaller diameter wire 80 producesa diffraction pattern which is sensed at detector 88 which may be of anyof the detectors illustrated in FIG. 4 8. The spacing of the diffractionpattern is measured and processed at computing system 90 as above, toprovide a precise measurement of the diameter of the raw, uncoated wire.Similarly, the beam from laser 84 incident on the coated wire produces asecond diffraction pattern which is sensed at detector 92 and processedat computer system 94 to provide a precise measurement of the diameterof the coated wire, that is, the combined diameter or thickness of thewire and the insulating coating thereonv The thickness of the insulatingcoating is obtained by applying the outputs of systems 90 and 94 to acomputer 96 in which the smaller measurement is subtracted from thelarger one, and the difference between these measurements is thendivided by two.

A read-out of the accurate coating thickness measurement obtained inthis manner may be used as a visual check to insure that the thicknessof the coating is proper. Preferably as herein shown, the signalproduced in computer 96 may be compared, as in a comparator Q8, againsta reference signal corresponding to the desired coating thickness. Inthe event the actual measured thickness is at variance with respect toits desired value, comparator 98 produces a control signal that isapplied to wiring coating machine 86 to control its operation in anymanner known in the art until a coating thickness of the desired valueis obtained. In addition, the signal output of system 90 may also beutilized in a similar manner to control the operation of thewire-forming apparatus (not shown) to obtain precise control over theraw wire diameter.

The system of FIG. 10 may be used to advantage in applications such asthe coating of teflon or plastic insulator onto a wire, or in anyoperation in which the diameter of small wires or yarns and theircoatings is to be measured and/or controlled in the manner described. I

Another technique for measuring the diameter of a yarn or a wire isschematically illustrated in FIG. ll which the beam from laser 24 iscaused to be reflected or scattered by yarn toward the laser or in anydirection around the yarn filament 101 of FIG. 12 to produce adiffraction image on a screen 100 rather than as in the previouslydescribed embodiments in which the light beam passes around the smalldiameter yarn to form the diffraction pattern on a distant screen.

The spacing between the bright (and dark) regions of the diffractionpattern obtained in this manner is again representative of the yarndiameter; that is, the expression for the yarn diameter of the system ofFIG. 11 is again d )tD/A Y, where d is the yarn diameter, A is thewavelength of laser 24, D is the distance between yarn 20 and screen100, and A y is the image line spacing of the diffraction patternproduced by the scattering of the laser beam by yarn 20.

The embodiment shown in FIG. 12 is a more detailed embodiment of thebasic principle illustrated by the system of FIG. 11. The laser beam isreflected or scattered off yarn 20 to form a diffraction image which isreflected by a mirror 102, and focused by a lens 104 onto a mirror 106.Mirror 106 is rotated by a motor 108 in a clockwise direction asindicated by the arrows. The rotating mirror 106 causes the diffractedimage to be swept across a mechanical slit 110 formed in a plate 112onto a detector 114 of one of the types previously described herein.Detector 114 generates an electrical signal representative of thediffraction pattern. In order to increase the signal-to-noise ratio ofthat signal, thereby to increase the accuracy of the yarn diametermeasurement, the repetitive signals produced at the output of detector114 are processed and thereby enhanced by applying the detector outputto one input of a signal averaging computer 116. The other input tocomputer 1 16 is a timing signal derived from a laser detector 118 whichis produced when mirror 106 is in a position to cause a beam produced bya laser 120 to be reflected normally onto the input of detector 118.Computer 116 adds all the repetitive diffraction image signals obtainedfrom detector 114 directly, but adds the noise signals only as thesquare root of the number of signals. Therefore, the signal-to-noiseratio increases only as where n is the number of scanning signals addedat computer 116.

The system of FIG. 12 is particularly useful in the measurement of thediameter of transparent or semitransparent yarn in which the forwarddiffraction pattern has a relatively low contrast between the dark andlight regions. Signal averaging, as performed in the FIG. 12 embodiment,will improve the contrast ratio, thereby increasing the accuracy of theyarn measurement. Another way of increasing the contrast ratio would beto dye the yarn a dark color to make it more opaque to the light beam.

The embodiment illustrated in FIG. 13 is another technique for derivingenhanced signals representing the spacing between the peaks or valleys,or bright and dark regions, of the diffraction pattern. As in theembodiment of FIG. 12 the diffraction pattern obtained by the scatteringof a laser beam by the yarn is focused by a lens 122 onto a rotatingmirror 124 which in turn causes the diffraction image to be swept acrossa plate 126 in which a slit 128 is formed. A detector 130 is placedbehind that slit and has its output connected to a voltage leveldetector 132 which may be a Schmitt trigger or zero-crossing detector.Voltage level detector 132 produces an output signal at times when theoutput signal of detector 130 exceeds a preset level. The output signalfrom detector 132 is applied to the input of a gate generator 134.Generator 134 produces a gate which is initiated by a signal fromdetector 132 and terminated by a succeeding signal from that detector.The width of the gate produced by gate generator 134 thus represents thetime interval between the peaks of the diffraction image signal. Thatgate is applied to one input of a pulse generator 136 which receivescontrol signals from an oscillator 138.

Oscillator 138 is also mechanically connected to a motor 140 whichcauses scanning mirror 124 to rotate. In operation, during the time thatthe gate from generator 134 is present, pulses from pulse generator 136are counted by the counter and stored in a display counter 142. Thenumber of pulses stored is directly proportional to the time the gate isopened and thus to the diameter of the yarn. A scan gate 144 provides agate to counter 142 to allow counter 142 to count the pulses from pulsegenerator 136 for a predetermined number (e.g., 100) of scans of thediffraction pattern, and to display the count or use the count signal togenerate a control signal as indicated above to control the yarnformation process. The use of a multiple number of scans improves theaccuracy of the yarn diameter measurement by increasing the accuracy ofmeasurement of the diffraction pattern spacing.

In the measurement system of FIG. 13, the accuracy of measurement issubstantially independent of the lateral movement of the yarn across thelaser beam so long as the yarn movement is slow as compared to the timeof the scan.

FIG. 14 illustrates the application of the concept of the presentinvention to test the sharpness of an edge during the process ofmanufacturing a sharp-edged object such as a knife, razor blade or thelike, or pointed objects such as needles, or the like, and to controlthe sharpness of the edge during that process. As shown in FIG. 14, abeam of monochromatic light produced by a laser 24 is passed through anopening 146 formed in a screen 148 and is caused to be incident upon thesharp edge 150 such as the edge of a knife. The interference patternproduced thereby is reflected or scattered off onto screen 148 and isthere observed and analyzed to test the sharpness of the edge.

A typical diffraction pattern for a sharp edge is shown in FIG. 15 inwhich the orientation of the knife edge is shown by the vertical brokenlines 152. The diffraction pattern obtained is illustrated by theintense horizontal narrow central line 154 with several less althoughwell-defined lines symmetrically formed both above and below the intensecentral line. For a dull edge the diffraction pattern obtained is thatillustrated in FIG. 16 in which the diffraction patterns appear as arandom, unsymmetrical distribution of dark lines formed on screen 148.The duller the edge being tested the wider will be the spread or therandom nature of the diffraction pattern observed.

This sharpness testing technique could be used to provide a visualinspection of the sharpness of the edge to aid in the blade sharpeningoperation as a quality control test. The process could also be used in ablade fabricating process or the like as a feedback and control elementby comparing the observed diffraction pattern against a reference,well-defined pattern of the type that would be produced by a sharp edge.The comparison of the actual and reference diffraction patterns may beused to control the blade-sharpening operation to ensure that all bladesfabricated have the desired degree of sharpness. Alternatively, when adull edge is sensed the sharpening process may be temporarily halted todiscover the reason for the improper forming of the edge. This procedurecould also be used to insure that the edge is properly oriented during asharpening operation since the bright lines on the diffraction pattern,formed when the laser beam is incident on the edge, are preciselyperpendicular to the orientation of the blade edge.

The apparatus and system of the present invention thus provide a highlyaccurate and reliable means for determining the thickness or diameter ofa fine object such as a wire, filament or strand of yarn. The methodrequires no physical contact of the measuring system and the filamentunder test, and thus can be used extremely fine filaments withoutcausing damage thereto, such as in the conventional methods usingmechanical feeler contacts. Furthermore, the optical measurement systemof the present invention is relatively simple in nature while stillproviding highly accurate measurement data.

The system and method of the invention can be used either solely tomeasure the diameter of the filament, or, in addition, can be used toprovide signals for controlling the formation of the filaments inconjunction with suitable feedback and control circuitry, thereby tomaintain the diameter of the filament at a precise predetermined value.

The basic principles of the invention have been illustrated in severalembodiments showing various means for measuring the spacing between thebright and dark regions of the diffraction pattern formed when the laserbeam passes around the small diameter filament. In another version ofthe invention the laser beam may be caused to be scattered or reflectedoff the yarn onto the diffraction plane to form the diffraction pattern.

Thus, while several embodiments of the present invention have beenherein specifically described, it will be apparent that variations maybe made therein without departing from the spirit and scope of theinvention.

I claim:

1. Apparatus for measuring the diameter of a fine filament, wire, or thelike comprising first laser means for irradiating the filament with abeam of light, first detecting means, scanning means for directing thediffraction pattern having alternating dark and light portions producedwhen said filament is irradiated by said beam to said first detectingmeans, signal averaging means having one input coupled to the output ofsaid first detecting means, second laser means directing a beam ontosaid scanning means, and second detecting means for producing a timingsignal when said beam from said second laser beam is reflected from saidscanning means normally to said second detecting means, the output ofsaid second detecting means being coupled to a second input of saidsignal averaging means.

2. The apparatus of claim 1, further comprising a plate having a narrowslit interposed between said scanning means and said first detectingmeans.

1. Apparatus for measuring the diameter of a fine filament, wire, or thelike comprising first laser means for irradiating the filament with abeam of light, first detecting means, scanning means for directing thediffraction pattern having alternating dark and light portions producedwhen said filament is irradiated by said beam to said first detectingmeans, signal averaging means having one input coupled to the output ofsaid first detecting means, second laser means directing a beam ontosaid scanning means, and second detecting means for producing a timingsignal when said beam from said second laser beam is reflected from saidscanning means normally to said second detecting means, the output ofsaid second detecting means being coupled to a second input of saidsignal averaging means.
 2. The apparatus of claim 1, further comprisinga plate having a narrow slit interposed between said scanning means andsaid first detecting means.